Japan's female Olympic judo athletes were beaten with bamboo swords and slapped by their coaches, officials have said.

A 15-strong group of judokas complained to the Japanese Olympic Committee last month that they had been subjected to physical punishment by the team's head coach.

The group, which included athletes who took part in the London Olympics, says head coach Ryuji Sonoda routinely abused them, slapping them in the face and hitting them with thick wooden swords, like those used in the Japanese martial art of kendo.

They also complained that some were forced to compete in matches while injured, reports said.

Image Caption:Head coach Ryuji Sonoda has not denied the accusations

"We have asked the All Japan Judo Federation to investigate the case and improve their methods if the charges are true," a JOC official said.

AJJF head Koshi Onozawa said the federation had told off Sonoda and other coaches, who had admitted several of the allegations and they had been told they must change their style or they will "will face a harsher punishment if a similar incident happens in the future".

Sonoda himself did not deny the allegations. "Until now I have been doing things the way I saw fit, but I will mend the things that need fixing," Kyodo News quoted him as saying.

Japan's women returned from London with one gold, one silver and one bronze medal in judo, well below their haul from the 2008 Beijing Games.

The case comes weeks after a Japanese schoolboy killed himself after repeated physical abuse from his basketball coach, an incident that has provoked a bout of national soul-searching over the way children are disciplined.

Under a law dating from 1947, teachers are not allowed physically to discipline their charges. However, there are no statutory punishments for those teachers who do so.

It is not the first time Japan's sporting world has been troubled with claims of violence - in 2007, a 17-year-old trainee sumo wrestler died after being badly beaten at the instigation of his trainer.

Speaking about the latest claims of brutality in sport, education and sports minister Hakubun Shimomura said it was time to reconsider the situation.

"It is time for Japan to change the idea that use of violence in sports including physical discipline is a valid way of coaching," he said.